DC835A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 835 LTC4441, MOSFET DRIVER LTC4441 DESCRIPTION Demonstration circuit DC835 is a MOSFET driver circuit Demonstration circuit DC835 can be easily modified to that is designed to facilitate adding a MOSFET driver to generate different gate drive output voltages by chang- an existing design. ing the voltage divider of the internal LDO regulator. Demonstration circuit DC835 is small and allows the The DC835 has a small circuit footprint. It is a high per- MOSFET driver LTC4441 to be added to an existing de- formance and cost effective solution for driving big sign in order to evaluate the performance. The board has MOSFETs in Telecom, Automotive and Industrial applica- a ground strip along one side that can be directly sol- tions. dered to source pins of an SO-8 or similar MOSFET. This Design files for this circuit board are available. Call assures the MOSFET driver will be most effective due to the LTC factory. low connection inductance between its output and , LTC and LT are registered trademarks of Linear Technology Corporation. MOSFET gate pin. QUICK START PROCEDURE Demonstration circuit DC835 is easy to set up to evalu- the power dissipation may overheat the part. Please ate the performance of the LTC4441. For proper meas- consult the LTC4441 data sheet for details. urement equipment setup refer to Figure 1 and follow 3. Set the Pulse Generator to 300kHz and turn the pulse the procedure below: output ON. NOTE: When measuring the input or output voltage wave- 4. Check for the proper output voltage of 6V and wave- forms, care must be taken to minimize the length of the forms as shown in Figure 3. oscilloscope probe ground lead. Measure the input or output voltage waveforms by connecting the probe tip directly across the PWM INPUT or G1 output and GND PROGRAMMING GATE OUTPUT VOLTAGE terminals as shown in Figure 2. 1. With power off, connect the input power supply to Vin Changing resistor R8 can program the output voltage at and GND. the OUT pin of the LTC4441. Do not change the value of 2. Turn the input power source on and slowly increase resistor R2. The 330kohm value is required for stability the input voltage. Be careful not to exceed 24V. of the internal LDO regulator. For more information, please refer to the LTC4441 data sheet. NOTE: Higher input voltage will cause higher power dissipation in the LTC4441 LDO regulator. If very big MOSFETs are used and switching frequency is high 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 835 LTC4441, MOSFET DRIVER ing circuit that may be used to circumvent the shortcom- BEWARE OF MOSFET DRIVER DELAYS ings of other PWM circuits leading edge blanking. Please refer to the LTC4441 data sheet for more details. MOSFET driver delays, which are on the order of 30ns, Demo Circuit DC835 has an input filter (R6 and C3) that need careful consideration. Some PWM controllers have is used to prevent ringing on the PWM INPUT line from built in leading edge blanking that prevents miss- causing false pulses at the output. This RC filter also triggering of the current comparator due to leading edge adds to the delay and needs to be taken into account. current spikes. If this blanking period is too short it may The RC filter can be removed if the PWM input line is not cover the additional delay caused by the MOSFET laid out correctly and is relatively short. driver. The LTC4441 has a built in programmable blank- 2